That was roughly the reasoning I was having, though not as technical, but I thought I might have some other way of achieving that result with Gimp.
I followed your tutorial below, and I removed the doubts by observing your .xcf.
Since they are different images I had to change some things, but practically I followed your tutorial.
The plugin that I used for layers and effects has some bugs, besides retune another mode to the selected overlay (returns softy light), it also returns all the modes in legacy format.
I still need to refine the effects in the layers, but the concept has been absorbed.
Thanks for the help, it was very enlightening, and the tutorial was super didactic!